PCD or PcBN tools for the wood industry

ABSTRACT

There is disclosed PCD or PcBN-tools for cutting wood containing 3 to 20 volume % binder phase based in Ni and/or Co. The binder phase comprises in solution, in weight percent, Co max 95, Ni max 95, Cr 5-45. In addition, nitrides and/or carbonitrides of Zr, Ti, Cr, Ta and/or V are evenly distributed in the structure in an amount of less than 50 volume %, preferably 5 to 40%, of the binder phase with a mean grain size less that 5 μm, preferably 0.3 to 4 μm.

BACKGROUND OF THE INVENTION

The present invention relates to new PCD (polycrystalline diamond) orPcBN (polycrystalline cubic boron nitride) tools with excellentproperties in tools for the wood industry. More particularly, theinvention relates to PCD or PcBN in which a corrosion and oxidationresistant phase has been distributed in the skeleton of diamonds orcBN-particles characterized by extensive bonding between the hardparticles. This corrosion and oxidation resistant phase is based oncobalt and/or nickel chrome.

Reconstituted wood products, such as medium density fiber board and chipboard, are, together with solid wood, the main raw materials in thefurniture industry. They are also used in the housing industry to someextent.

These products are machined with a variety of tool materials, from highspeed steel to cemented carbide to polycrystalline diamond. A leadingrole is being played by tools made with cemented carbide and PCD orPcBN-tools.

The composition of PCD or PcBN used for woodworking tools consistgenerally of diamonds or cBN with cobalt as an intergranular phase.Sometimes small amounts of other carbides, nitrides or carbonitrides areadded.

The constitution of the PCD are built up by one or severallayers/translayers with different compositions regarding diamondcontents and cobalt.

Abrasion has been thought to be the primary mechanism of tool wear whenmachining reconstituted wood products and solid wood. Recent work hasproven that chemical mechanisms such as corrosion and oxidation play asignificant role in the degradation of cutting edges, as the temperatureincreases dramatically during the machining process.

The chemical degradation of existing PCD and PcBN-tools is at least atwo stage process when machining wood products.

At first, the degradation occurs at a low temperature (300-500° C.), inthe early period of cutting. As the tool temperature rises, the woodproducts decompose and numerous chemicals are introduced in the cuttingenvironment. More than 200 different compounds have been identified uponthe destructive distillation of wood. The machining of medium densityfiber board and particle board produces even more decompositionproducts. These products contain also a binder such as urea,formaldehyde, wax and glue fillers and extenders and possibly chemicalsadded as flame retardants. The decomposition products formed are highlycorrosive and attack the cobalt-phase that fills the voids between thehard particles. When this occurs, the diamond-grains loses the sites ofthe diamond-diamond contact due to the high mechanical stresses and thecutting edge loses its sharpness and its cutting capability.

As the temperature rises above 500° C., the decomposition products areviolatised and removed, but degradation of the cutting edge continues byoxidation of the cobalt phase in air. The oxides formed are readilyremoved by mechanical action, resulting in a fast degradation of thesharpness of the cutting edge.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of this invention to avoid or alleviate the problems ofthe prior art.

It is further an object of this invention to provide PCD or PcBN toolswith excellent properties in tools for the wood industry.

It is an aspect of the invention to provide a tool for cutting woodcomprising polycrystalline diamond or polycrystalline boron nitride in 3to 20 vol-% binder phase based on Ni and/or Co wherein said binder phasecomprises in solution, in weight-%, Co max 95, Ni max 95, Cr 5-45 andadditives of nitrides and/or carbonitrides of Zr, Ti, Cr, Ta and/or V inan amount of less than 50 volume-% of the binder phase with a mean grainsize less than 5 μm with an even distribution in the structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The present invention relates to new types of PCD with excellentcorrosion and oxidation resistance properties particularly satisfyingthe different needs of the wood industry.

Resistance to corrosion and oxidation has been achieved by alloyingcobalt and/or nickel with chrome and distributing it in thePCD-skeleton.

The material according to the invention comprises 3 to 20 vol-% of Coand/or Ni with additives of nitrides and/or carbonitrides of Zr, Ti, Cr,Ta and/or V. The amount of said additives should be less than 50volume-%, preferably 5 to 40% of the binder phase. The mean grain sizeshall be less than 5 μm, preferably 0.3 to 4 μm with an evendistribution in the structure.

In one embodiment when sharp edges are required, e.g., for finishing ofhard wood as hickory or teak for fine surface smoothness, the mean grainsize of said diamonds is <5 μm, preferably <2 μm, most preferably <1.5μm. The content of the binder shall be 5 to 20 volume-%, preferably 6 to11 volume-%.

In an alternative embodiment when the wear properties should beoptimized, e.g., for machining medium density fiber board and chip boardthe mean grain size of said diamonds should be between 5 and 20 μm,preferably 5 and 8 μm. The content of the binder shall be 3 to 12volume-%, preferably 4 to 8 volume-%.

In both embodiments the diamond grain size distribution may be unimodal,bimodal, trimodal, etc.

The binder phase comprises in solution in weight-%, Co max 95, Ni max 95and Cr 5-45 and, in addition, W max 30, Mo max 15, Al max 2, Mn max 10,Si max 2, Cu max 10, Fe max 20, Ag max 5 and Au max 10. In a preferredembodiment, the binder phase is nickel based and comprises in solution,in weight%, Co max 30 and Mo 1-6. In another preferred embodiment, thebinder phase comprises in solution, in weight-%, Co max 30-70 and Mo1-6.

The materials according to the invention are manufactured by powdermetallurgical methods known per se namely mixing, compaction andsintering in the diamond stable area.

The material according to the invention is particularly useful formachining of particle board, chip board, medium density fiber board anddry woods. For cutting of particle board, chip board and medium densityfiber board the binder phase content shall be 3 to 12 volume-% and forcutting of solid woods the binder phase content shall be 5 to 20volume-%.

The invention is additionally illustrated in connection with thefollowing Examples which are to be considered as illustrative of thepresent invention. It should be understood, however, that the inventionis not limited to the specific details of the Examples.

EXAMPLE 1

PCD-tools according to the invention were manufactured with a diamondcomposition of: 4 volume-% of diamond grain size between 1 and 3 μm, 18volume-% of diamond grain size 4-7 μm, 71 volume-% of diamond grain size8-12 μm. TiN was added in an amount of 1 volume-% of the total mix. Thebinder content was 6 volume-% with a composition of 66% Co, 25% Ni, 9%Cr. The powder mixture was milled in a ball mill with ethanol andcemented carbide milling balls for four hours. The milled powder wasdried in a rotating vessel and granulated in a 200 mesh size sieve. Theprecompaction of the powder was performed onto a disc of a straightgrade cemented carbide (6% Co). The sintering was conducted under suchtemperature and pressure conditions where the diamonds are stable. ThePCD-s were cut out by laser cutting into a conventional rectangularcutter shape with a cutting angle of 65° and ground to final shape.

EXAMPLE 2

A PCD-tool according to prior art was tested against a PCD according tothe invention, example 1. The test was performed on a turning test onmedium density fiber board discs.

    ______________________________________                                        Rotating speed         550 rpm                                                Cutting depth                        0.13 mm                                  ______________________________________                                    

The rake and clearance angles were 15 and 10 degrees, respectively.

Three samples of each tool material were tested.

The edge radius for all tools was 2 μm.

The edge wear and the surface finish of the chip board were measuredafter each sample cut, a total of fifteen, 19 mm discs for a totallength of cut of approximately 6883 m. The following result was obtainedexpressed as parallel, F_(p), and normal, F_(n), tool force components,in Newton, as a function of sample cut in number of discs.

    ______________________________________                                                       Number of discs                                                               0    5        10     15                                        ______________________________________                                        According to the invention                                                    F.sub.n (in Newton)                                                                            46.7   51.2     53.4 55.6                                    F.sub.p                      95.6      89.0                                                                       100.1                                                                               104.5                               According to the invention                                                    F.sub.n          47.6   57.8     62.3 71.2                                    F.sub.p                      97.9       93.4                                                                       106.8                                                                             113.4                                ______________________________________                                    

The tool of the material according to the invention gave a bettersmoothness of the surface in comparison with the prior art tool.

The invention has been described with reference to PCD tools but it isobvious that it can be applied also to tools with PcBN.

The principles, preferred embodiments and modes of operation of thepresent invention have been described in the foregoing specification.The invention which is intended to be protected herein, however, is notto be construed as limited to the particular forms disclosed, sincethese are to be regarded as illustrative rather than restrictive.Variations and changes may be made by those skilled in the art withoutdeparting from the spirit of the invention.

I claim:
 1. Tool for cutting wood comprising hard particles consistingessentially of polycrystalline diamond or polycrystalline boron nitrideand 3 to 20 vol-% of a binder phase based on Ni and/or Co wherein saidbinder phase comprises at most 95 weight-% Co, at most 95 weight-% Ni, 5to 45 weight-% Cr and 5 to 40 vol-% of the binder phase of nitridesand/or carbonitrides of Zr, Ti, Cr, Ta and/or V with the mean grain sizeof said nitrides and/or carbonitrides being less than 5 μm and saidnitrides and/or carbonitrides being evenly distributed in the binderphase, the mean grain size of the diamond or polycrystalline boronnitride being between 5 and 20 um.
 2. The tool of claim 1 wherein saidbinder phase further comprises at most 30 weight-% W and at most 15weight-% Mo.
 3. The tool of claim 1 wherein said binder phase furthercomprises at most 30 weight-% Co and from 1 to 6 weight-% Mo.
 4. Thetool of claim 1 wherein said binder phase further comprises 30-70weight-% Co and from 1 to 6 weight-% Mo.
 5. The tool of claim 1 whereinsaid binder phase further comprises at most 2 weight-% Al, at most 10weight-% Mn, at most 2 weight-% Si, at most 10 weight-% Cu, at most 20weight-% Fe, at most 5 weight-% Ag and at most 10 weight-% Au.
 6. In thecutting of solid dried wood with a tool, the improvement comprisingusing the tool of claim 1 with a binder phase content of 5-20 % byvolume.
 7. In the cutting of solid dried wood with a tool, theimprovement comprising using the tool of claim 1 with a binder phasecontent of 3-12 vol-%.
 8. The tool of claim 1 wherein the nitridesand/or carbonitrides have a mean grain size of 0.3 to 4 μm.
 9. The toolof claim 1 wherein the binder content is from 5 to 20 volume %.
 10. Thetool of claim 9 wherein the binder content is from 6 to 11 volume %. 11.The tool if claim 1 wherein the binder content is from 3 to 12 volume %.12. The tool of claim 1 wherein the mean grain size of the diamond orboron nitride is from 5 to 8 μm.
 13. The tool of claim 12 wherein thebinder content is from 4 to 8 volume %.